Radio frequency (RF) filters and duplexers have been essential components of communication systems. High selectivity, low insertion loss, compact size, ability to handle large signals (power handling), high linearity, manufacturability, and low cost may be some of the important desired features for RF filters and duplexers.
The requirements for RF filters and duplexers have become more stringent in light of new communication standards where information channels and frequency bands are closer to each other, new communication devices such as smartphones where the footprint and cost of all components must be very small as more components are needed in support of multiple standards and applications, and co-existent communication systems where multiple communication transmitters and receivers work simultaneously.
In radars, the relatively strong transmitter waveform should be isolated from radar's sensitive receiver that is designed to detect relatively small reflected waveforms. Certain level of isolation may be achieved by using two separate antennas for the transmitter and the receiver, or a circulator that interfaces a common antenna to the transmitter and the receiver. The isolation provided by such conventional methods may not be sufficient.
What is needed are tuning feed-forward cancellation schemes that may be added to reduce the level of unwanted signals and to enhance the isolation between desired blocks within a system. Cancellers may remove the need for selective filtering or relax the filtering requirements.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present disclosure as set forth in the remainder of the present application with reference to the drawings.